Controlling diabetes with a cellular GPRS-linked glucometer-pedometer

ABSTRACT

The Cellular GPRS system includes a cellular-based Glucometer (CBG) for blood glucose monitoring, a pedometer for exertion measurement, combined with user-entered dietary or other diabetes-relevant information. Data from all inputs is transmitted over a cellular network, using a GPRS or other wireless link. The data is preferably stored in the device prior to being transmitted wirelessly over the cellular airway to a central computer server. The remote computer server will evaluate the data received and respond with a data packet (making recommendations on further glucose measurement, exercise, diet, insulin requirements or other).

RELATED APPLICATIONS

This application claims priority to U.S. application Ser. No.12/426,984, filed Apr. 21, 2009 (pending, allowed), which in turn claimspriority to U.S. Provisional Application No. 61/046,881, filed Apr. 22,2008.

BACKGROUND

In managing diabetes, it is well known that wellness is related toglucose level, and that blood glucose level is affected by exertionlevel (calories consumed) and diet. The calories consumed are related tothe speed and force of movement and the mass of the subject. Walkinguphill consumes more calories than downhill, or on a level, and runningconsumes more per unit time than walking. Existing pedometers do notaccount for vertical vs. horizontal acceleration, and require aparticular orientation to differentiate these two axes to therebydetermine steps taken and calorie expended (when the weight of thesubject is known). This makes them difficult to use, and affects theaccuracy of the results (if they are oriented wrongly and this is notdetected).

Existing glucometers (which determines blood glucose level) andpedometers do not interact so as to correlate results from theglucometer with calories expended (based on the pedometer results). Suchcorrelation can be used effectively to adjust the actions the subjecttakes, i.e., a low glucose level can be the result of exertion, and thesubject could be instructed to reduce activity level rather thanconsuming carbohydrates.

One design of existing glucometers employs glucose dehydrogenase togenerate electrons on a strip covered with blood, and the change involtage across the strip is measured over time to determine glucoseconcentration. Resistance across the strip drops over time due to thechemistry of the strip and the increase in the product oldieenzyme-catalyzed reaction. Measurement of the corresponding voltage dropis correlated with known blood glucose concentrations to determine thesubject's blood glucose concentration.

The disadvantages of such glucometers include that they are noisesensitive, as voltage is calculated directly from the current flow.Noise-resistant designs are thus desirable.

There is also a need to measure exertion levels of the subject, thenreadily transmit data from glucometers and exertion measurement devices(e.g., pedometers) to a monitor, who can determine what instructions toprovide the patient to maintain blood glucose at optimal levels. Thetransmission medium should be inexpensive and widely used, to avoidadded costs.

SUMMARY

The Cellular GPRS system includes a cellular-based Glucometer (CBG) forblood glucose monitoring, a pedometer for exertion measurement, combinedwith user-entered dietary or other diabetes-relevant information. Datafrom an inputs is transmitted over a cellular network, using a GPRS orother wireless link. The data is preferably stored in the device priorto being transmitted wirelessly over the cellular airway (using a GPRSor other wireless communication link rather than a Bluetooth orvoice-based link) to a central computer server. The remote computerserver will evaluate the data received and respond with a data packet(making recommendations on further glucose measurement, exercise, diet,insulin requirements or other) which can be read on a cell phone or PDAor otherwise.

The glucometer design preferably involves a blood-glucose strip, wherecurrent across the strip, rather than voltage, is correlated with bloodglucose levels. The pedometer design is most desirably a three-axisaccelerometer, capable of determining and monitoring movement in anydirection. This design allows the device to determine if the subject iswalking or running.

Other data (particularly relating to diet and insulin use) can also beinput and transmitted. The data as a whole can be evaluated at thecentral monitoring station, and specific recommendations to the patient(including, recommendations on insulin injection, need to eatcarbohydrate, exercise level) can be readily made. These recommendationscan be displayed on a cell phone or PDA, for immediate processing andaction by the patient.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of the functions of reading and analyzing aglucose test strip.

FIG. 2 is a block diagram of the functions of reading and analyzing aglucose test strip and transmitting the results through a GPRS.

DESCRIPTION

The CBG electronics arc preferably contained in a small housing that caneasily be clipped to the shirt, pants, purse, or placed into a pocket.The electronics consist of a LCD display, cellular GPRS radio,glucometer, and accelerometer (used for the pedometer function). The CBGmodule is preferably powered by a rechargeable lithium ion battery so asto operate several days between charges.

The CBG pedometer can monitor activity of the user throughout the day.Along with information such as distance traveled, the pedometer can alsoaccess the effort expended during activity. The pedometer candifferentiate between a brisk walk, run, long strides, or casualstrolls. This information creates a more accurate assessment of caloriesexpended during activity. Suitable pedometers are discussed below.

Referring to FIG. 2, the glucometer is continuously powered and iscontinuously monitoring activity with the pedometer (14). Upon insertionof a blood glucose strip (2), it commences a blood glucose reading. Inthe glucometer of the invention, the current is not measured directly.

Using existing glucose monitoring strips, the glucometer requires 220millivolts maintained across the two electrodes. One of the electrodesis a reference electrode and the other is the working electrode. Thereference electrode is connected to electrical ground (common), and theworking electrode is maintained at 220 mV. A microprocessor controlledvoltage source (e.g., a Digital to Analog Converter—(DAC), produces avoltage which is connected to the working electrode through a resistorof known value. A volt meter (e.g., an Analog to Digital Converter—ADC)is also connected to the working electrode to ensure that the 220 mV isalways maintained.

When a blood sample is placed on the test strip, the resistance of thestrip immediately drops, causing current now. This causes the voltage onthe working electrode to drop, which is sensed by the ADC and isimmediately compensated for by the DAC. Over the next 10 seconds theresistance of the strip will first decrease for about 9 seconds, andthereafter, will increase causing the current flow to decrease. The ADCcontinuously monitors this change and signals the DAC to adjust theoutput voltage to maintain 220 mV on the working electrode.

During seconds 9 through 10, the calculated current values arc averagedand this average is used to derive the actual blood glucose value.Because the voltage produced by the DAC is always known, the seriesresistance is known, and the working electrode voltage of 220 mV isknown, the current through the strip can be accurately calculated. Theblood glucose value is a direct function of the current flowing throughthe test strip and is adjusted for the ambient temperature during thetest, and the strip manufacturing lot variance.

Referring to FIGS. 1 and 2, when a Blood Glucose Test Strip (2) isinserted into the Test Strip Receptacle (3), the Microcontroller (8)recognizes the insertion of the strip. The glucometer electronicsperforms the glucose strip reading function as depicted in FIG. 1:

-   -   1. Exactly 200 mV potential is produced across the working and        reference electrodes of the strip.    -   2. When blood is applied to the strip, current begins to flow        into the strip.    -   3. After 9 seconds an average of the current is calculated        continuously until 10 seconds is reached.    -   4. The average current value directly correlates to the blood        glucose level.    -   5. This value is further compensated for temperature variations        and test strip production lot variations.    -   6. The microcontroller then executes the steps described above        to accurately read the current flowing into the test strip. Over        time, the resistance of the test strip continues to increase        requiring the DAC to decrease its output.    -   7. Because the voltage output of the DAC is known, the fixed        resistance is known, and the 220 mV reference is known, the        current flowing into the test strip can be derived as:        I _(strip)=(V _(DAC) −V _(ref))/R

This measurement technique provides a very accurate high resolutioncurrent value with low noise, high repeatability, and a very widedynamic current range without additional support electronics.

Once the Microcontroller (8) of FIG. 2 has confirmed that the bloodsample has been acquired, the following occurs:

-   -   1. The digital representation of the Blood Glucose Test Strip        (2) current is sampled and stored at regular intervals over a        fixed period of time.    -   2. The slope of the current is noted. If the slope is trending        in the wrong direction, the test is aborted with an error.    -   3. The Temperature Sensor (6) value is acquired by the        Microcontroller (8) at regular intervals and is averaged over        the entire test time.    -   4. A signal is sent to the Cellular GPRS (10) indicating that a        test is in progress, which can in turn relay it to a central        server.    -   5. The LED (7) begins to flash rapidly to indicate that a test        is in progress.

At the completion of the test, the blood glucose value is determined asa function of the following:

-   -   1. The slope of the digital representation of the Blood Glucose        Test Strip (2) sampled current verses time.    -   2. The average temperature during the test.    -   3. The test strip lot calibration value which is used to access        a library stored within the Microcontroller (8) to compensate        the calculated blood glucose value.    -   4. The LED (7) remains solid for 2 seconds and then turns off to        indicate that the test is completed and that it is now safe to        remove the test strip. The blood glucose value is shown on the        LCD display.    -   5.

The final determined blood glucose value is then evaluated by theMicrocontroller (8) to ascertain it is within an expected range or ifthe blood sample was actually a standard solution for test andverification. The results of the test are then sent to the GPRS (10)which in turn, relays this information to the server (11), for analysis.

If the GPRS link is not available, then the time of the blood glucosereading and the value of the reading are stored in the non-volatilememory of the glucometer. The memory can store up to 1000 readings. Whenthe GPRS becomes available, the readings are then transferred to itsmemory.

The Microcontroller (8) enters into a low power sleep state and does notawaken until a new test strip is inserted, or is triggered to wake upfrom movement detected by the accelerometer.

FIG. 3 shows the separate operation of a three-axis pedometer, suitablefor use as the accelerometer of FIG. 1. The device measures accelerationin three separate axes, and can measure human movement (walking,jogging, running) irrespective of orientation. By determiningacceleration in multiple axes, and monitoring time, it can determinedirection of movement. In walking/jogging/running, there is a verticalcomponent of acceleration of shorter duration and with a differentprofile over time, than the acceleration component in the direction oftravel. Also, in jogging or running, the vertical and direction oftravel components have a different profile from walking, or from othermotion (like driving a car). If there is no acceleration. componentinput, the device goes into a power-saving sleep mode.

From the acceleration information, the distance traveled by the user isdetermined, and using this information, with the weight of the user, theenergy expended (as calories) are determined, and then led back to themicrocontroller 8 (then to a GPRS and server) as shown in FIG. 2.

The microcontroller 8 is responsible for correlating data from theglucometer and pedometer. The results can be displayed on a cell phone(or an outside screen of a GPRS) and can be used a number of differentways, one of which is determining whether the correlated results arewithin or outside of a known index of such values. The index has beenestablished based on the known relationship between exercise (consumingcalories) and lowering blood glucose levels. Thus, for example, if thecalories consumed over a given period correlate with a predicted drop inblood glucose, as long as the glucometer indicates that the level iswithin the index guidelines, no action by the user need he taken. But ifthe blood glucose level is outside the index guidelines, actions from“stop exercising” to “eat” or “take insulin” can be flashed on thedisplay for the user to act on.

A related device which uses or relies on the various componentsdescribed above is a combination glucometer adapter/pedometer, where theadapter can receive and decode input from a particular make/model (orseveral different makes/models) of glucometer. The results from thepedometer and the glucometer are still correlated and compared to theindex, and displayed, as described above.

Pedometer Function

A 3 axis accelerometer (14) is used as the foundation for the pedometerfunction. The 3 axis accelerometer eliminates the need to orient the itto obtain an accurate reading. The microcontroller automaticallydetermines the horizontal and vertical axis.

By using mathematical relationships between acceleration and time,distance traveled is calculated. Also calculated is the number of steps,pace, stride, effort (vertical acceleration), and calories expended(given body weight). The microcontroller acquires acceleration data fromthe accelerometer every 100 mS. This data is processed and averaged andsend to the GPRS for transmission.

Power Management

The glucometer and pedometer are powered from a lithium ion batterywhich is rechargeable. This battery technology does not exhibit “memoryeffect” which is ideal for long run times. The charge circuit (12) willbring the battery to a full charge in less than 5 hours for a completelydischarged battery. Typically the charge time is around 2 hours. TheGlucometer or pedometer can also be charged from a standard mini-USBconnector which can be plugged into a computer (or any USB power source)for power or a wall transformer. The run time between charges on averageis about 1 week.

The glucometer and pedometer should always be powered. To conservepower, they operate at different levels of power conservation dependingupon the activity as follows:

1. Active Mode:

-   a. The glucometer and pedometer have an active GPRS radio link is    actively transmitting data.-   b. A cell phone can request that data is sent via the GPRS radio.-   c. The accelerometer is checked for motion.    2. Sleep Mode:-   a. The GPRS radio is in a low power listening mode but is not    communicating.-   b. The accelerometer is accessed every 100 mS detecting motion.    3. Deep Sleep Mode:-   a. The GPRS radio is in sleep mode.-   b. The accelerometer is accessed every minute due to minimal motion.    4. Hibernate:-   a. The GPRS radio is in sleep mode.-   b. The accelerometer is accessed every 10 minutes due to no movement    detected for 5 minutes while in the Sleep Mode.    The glucometer progresses to the Active mode once the accelerometer    detects motion or a blood glucose reading has been taken. As glucose    or movement activities decrease, the “Device” descends into the    deeper modes of sleep to retain power.

It should be understood that the terms and expression and examples usedherein are exemplary only, and not limiting, and that the scope of theinvention is defined only in the claims which follow and includes allequivalents of the subject matter of those claims.

What is claimed is:
 1. A method of controlling a subject's diabetescomprising: determining blood glucose level in a blood sample from thesubject using a blood glucose test strip which is contacted with theblood sample and wherein current which is passed through the test stripat a constant voltage maintained across two electrodes is continuouslymeasured, where one of the electrodes is connected to ground and theother electrode, which is the working electrode, is maintained at 220mv, and wherein a digital representation of the current is sampled andstored at regular intervals over a fixed period of time, following thecontact with the blood sample, during which time the current flow firstrises then falls as the resistance of the test strip drops then risesand such current flow changes are sensed and the voltage on the workingelectrode is maintained at 220 mv during said fixed period, and theslope of the digital representation is used in determining the bloodglucose level; determining the subject's exertion level based ondetection of motion patterns from a 3-axis accelerometer, associatedwith the subject which, based on the acceleration patterns from thethree axes, can distinguish walking from jogging from riding in a car;continuously transmitting the blood glucose level and exertion level toa monitor for analysis over a cellular GPRS link, wherein the combinedeffect on the subject of the exertion level and the blood glucose levelare analyzed to determine whether the monitor recommends one or more of:increase or decrease the exertion level, eat carbohydrates, andadminister insulin; and receiving the recommendations from the monitorby the subject over the cellular GPRS link.
 2. The method of claim 1further including the subject acting on the recommendations by one ormore of: performing another blood glucose level assay; increasing ordecreasing exertion level; injecting insulin; or eating carbohydrates.3. The method of claim 1 wherein the monitor is a computer server or ahealth professional.
 4. The method of claim 1 wherein the patient entersinformation about the food(s) recently consumed.